It is often desirable to control the level of a liquid in a sump or water tank, such that a pump is activated when the liquid rises above a predetermined level and deactivated when the liquid falls beneath a second predetermined level. There are numerous level control systems in the prior art, many of which utilize mechanical or moving parts such as rubber diaphragms, springs, rods, floats or balls which parts have a tendency to wear out or malfunction. Other prior art systems operate on electrical or optical principles, in which electrical or optical probes are positioned in the tank and used to sense the level of liquid therein, and thereby control a liquid pump. However, such prior art systems are sensitive to humidity and moisture, and in addition to voltage levels in the sensing circuit, such that they often need to be adjusted and may produce erroneous control signals under certain conditions.
The present invention substantially reduces or eliminates such problems by providing a solid state electronic sensing and control system which has no mechanical or moving parts and which operates on simple and electrically predictable principles.